The present invention relates to a method of manufacturing a color filter, and more particularly, to a method of increasing the adhesion of color filters on the semiconductor wafer.
Charge-coupled device (CCDs) have been the mainstay of conventional imaging circuits for converting light into an electrical signal. The applications of CCDs include monitors, transcription machines and cameras. Although CCDs have many advantages, CCDs also suffer from high costs and the limitations imposed by its volume. To overcome the weakness of CCDs and reduce costs and dimensions, a CMOS photodiode device is developed. Since a CMOS photodiode device can be produced by using conventional techniques, both cost and the volume of the sensor can be reduced. The applications of CMOS photodiodes include PC cameras, digital cameras, etc.
Whether the image sensor device is composed of a CCD or CMOS photodiode, the incident light must be separated into a combination of light of different wave lengths, for example, red, blue and green light. Then, the light is received by corresponding sensor devices and is transformed into electrical signals so as to obtain the original color of incident light by returning the electrical signals. Therefore, a color filter array must be formed on each photosensor device. Currently, color filters are produced by either patterning photosensitive resins using a photo-etching process with the resultant patterns being dyed by a dyeing material, or a photoresist containing dyeing material is directly used to produce color filters.
Please refer to FIG. 1 to FIG. 6. FIG. 1 to FIG. 6 are cross-sectional diagrams of manufacturing a color filter array on a photosensor device according to the prior art method. As shown in FIG. 1, the semiconductor wafer 10 contains a silicon substrate 12 and a P-well 14 positioned on the silicon substrate 12. The photosensor device contains a plurality of CMOS photodiodes and each photodiode contains a metal-oxide semiconductor (MOS) transistor (not shown) positioned on the P-well 14. A photosensor area 18 is formed on the P-well 14 to electrically connect with the MOS transistor. The MOS transistor is a complementary metal-oxide semiconductor (CMOS) transistor composed of an NMOS transistor and a PMOS transistor and functions as a CMOS transistor sensor. The semiconductor wafer 10 also contains a plurality of field oxide layers or shallow trench isolation (STI) structures 16 positioned on the silicon substrate 12 that surrounds the photosensor area 18. The STI structures 16 act as a dielectric insulating material to prevent short circuiting due to contact between the photosensor areas 18 and other units.
First, a passivation layer 20 is formed on the surface of the semiconductor wafer 10 that covers each photosensor area 18. Next, as shown in FIG. 2, a red color filter layer (not shown) is formed on the surface of the semiconductor wafer 10. The color filter layer is composed of a positive type photoresist containing a red dye in a large amount (dry weight) of 10 to 50 wt %. A pattern-exposure process is used to form patterns of red color filters in the color filter layer, then the exposed portions of the filter layer is removed to form each red color filter 22. For increasing the effect and reliability of color filters, an ultraviolet (UV) light irradiation and heating process is performed after the formation of the red color filters 22. The UV light used has a wavelength of 320 nm or less at a quantity of 20 J/cm2 or less. The heating process is preferably performed in an inert atmosphere, for example, in nitrogen (N2) for suppressing the oxidation of the photoresist material. The starting temperature of the heating process is between a range of 60xc2x0 C. to 140xc2x0 C. Then, an average increasing temperature rate used in the heating process is 1.5xc2x0 C./sec. The end temperature of the heating process is between a range of 160xc2x0 C. to 220xc2x0 C.
Next, green and blue color filters are formed by repeating the above-mentioned processes. As shown in FIG. 3, a green color filter layer 24 is formed on the surface of the semiconductor wafer 10. The color filter layer 24 is composed of a positive type photoresist containing a green dye in a large amount (dry weight) of 10 to 50 wt %. As shown in FIG. 4, a pattern-exposure process is used to form patterns of green color filters in the color filter layer 24, then the exposed portions of the filter layer 24 is removed to form each green color filter 26. For increasing the effect and reliability of color filters, a UV light irradiation and heating process is also performed after the formation of the green color filters 26. The UV light used has a wavelength of 320 nm or less at a quantity of 20 J/cm2 or less. The heating process is preferably performed in an inert atmosphere, for example, in nitrogen (N2) for suppressing the oxidation of the photoresist material. The starting temperature of the heating process is between a range of 60xc2x0 C. to 140xc2x0 C. Then, an average increasing temperature rate used in the heating process is 1.5xc2x0 C./sec. The end temperature of the heating process is between a range of 160xc2x0 C. to 220xc2x0 C.
As shown in FIG. 5, a blue color filter layer 28 is formed on the surface of the semiconductor wafer 10. The color filter layer 28 is composed of a positive type photoresist containing a blue dye in a large amount (dry weight) of 10 to 50 wt %. As shown in FIG. 6, a pattern-exposure process is used to form patterns of blue color filters in the color filter layer 28, then the exposed portions of the filter layer 28 is removed to form each blue color filter 30. For increasing the effect and reliability of color filters, a UV light irradiation and heating process is also performed after the formation of the blue color filters 30. The UV light used has a wavelength of 320 nm or less at a quantity of 20 J/cm2 or less. The heating process is preferably performed in an inert atmosphere, for example, in nitrogen (N2) for suppressing the oxidation of the photoresist material. The starting temperature of the heating process is between a range of 60xc2x0 C. to 140xc2x0 C. Then, an average increasing temperature rate used in the heating process is 1.5xc2x0 C./sec. The end temperature of the heating process is between a range of 160xc2x0 C. to 220xc2x0 C. The color filter array of a photosensor device produced by the prior art method is then completed.
As the resolution of the photosensor device increases, the dimension of each element in the photosensor device correspondingly decreases. Due to reduction of color filter dimension, the contact area between the color filter and the passivation layer is decreased and results in adhesion weakness. As well, the thickness of the color filter is also decreased to lead to the occurrence of cross-talk in the photosensor device.
It is therefore a primary objective of the present invention to provide a method of manufacturing a color filter for increasing the contact area between the color filter and the passivation layer. Furthermore, the adhesion between the color filter and the passivation layer is enhanced so as to prevent stripping of the color filter.
The present invention provides a method for increasing the adhesion of a color filter on a semiconductor wafer. The semiconductor wafer comprises a substrate, a plurality of MOS transistor sensors positioned on the substrate, and a plurality of insulators formed between two MOS transistor sensors on the substrate. The present invention first involves forming a dielectric layer on the semiconductor wafer, which covers each MOS transistor sensor and each insulator. Thereafter, a passivation layer is formed on the dielectric layer, and a plurality of recesses are formed in the passivation layer and positioned above a corresponding MOS transistor sensor. Finally, a color filter is formed in each recess. The recess is used to increase the contact areas between the color filter and the passivation layer so as to prevent stripping of the color filter.
The color filter produced by the present invention method uses a plurality of recesses formed in the passivation layer to increase the contact areas between the color filter and the passivation layer. Furthermore, the adhesion between the color filter and the passivation layer is enhanced so as to prevent the stripping of the color filter.
These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment, which is illustrated in the various figures and drawings.